Heretofore, in oil-based ball-point pens, for suppressing a so-called sagging phenomenon in which an ink leaks from the top end of a tip, point seepage at the tip or blobbing phenomenon of contaminating the paper surface due to a simple structure thereof, problems were solved by the approach of controlling the viscosity of the ink to about 10,000 mPa·s, restricting the ink discharge mechanism in view of the structural design such as the inner diameter of a ink containing tube, clearance at the pen tip, etc., adding inorganic filler particles to the ink thereby providing thixotropy, or adding a certain polymer to give an effect on the ink discharge. However, as mixed solvents comprising components such as less volatiling aromatic type glycol ether and aromatic type alcohol are usually used for the ink solvent, no remarkable progress has been made other than the procedures described above.
In view of the above, an object in the first aspect of the invention is to provide an ink composition for a ball-point pen that enables suppression of the blobbing phenomenon by controlling the volatility of the ink solvent to prevent excessive drying on the ball surface and suppressing the blobbing phenomenon by controlling the internal cohesion force of the ink.
Further, in the commercially available oil-based ball-point pens described above, the solvent comprises a mixture of 2-phenoxy ethanol and benzyl alcohol, and an oil-based ball-point pen using, as the main solvent, a solvent represented by the chemical structural formula (1):
where R1, R2, and R3 each represents independently H or CH3 has not yet been commercially available.
While seeking a smooth writing feel, rapid ink penetration to the writing surface, a good drying property at the pen tip, etc., the present inventor has studied ink compositions using, as a main solvent, a solvent of chemical structural formula (1) (refer to Japanese Patent Application No. Hei 12-232004 which was not laid-open at the time of filing Japanese Patent Application No. 2002-275807 as the basis for claiming the priority of the present application).
Further, in the conventional oil-based ball-point pens, as it is difficult to use a pigment in the oil-based ball-point pen, light fastness was usually ensured by using, for example, a metal-containing dye in order to enhance the light fastness. However, a pigment is excellent in view of the fastness.
Further, in the conventional oil-based ball-point pens, as a high viscosity ink is used, it has not been adopted, to provide back-flowing structure, an ink follower for preventing back flow, or providing a back-flow-preventive mechanism at a joint portion connecting a tip and an ink containing tube in order to prevent back flow.
The present inventor had reached that idea that, in the oil-based ball-point pen using the ink composition using the solvent of the chemical structural formula (1) as a main solvent, the flowability of the solvent is high and air tends to intrude from the pen tip and cause disadvantages it is necessary to mount a back-flow-preventive mechanism. Further, with the intention of using a pigment for light fastness, the inventor has made a study to provide an oil-based ink composition favorable in the fastness, coloring property and dispersion stability of the pigment, in an oil-based ball-point pen that holds an ink composition using the solvent of the chemical structural formula (1) as a main solvent, and a back-flow-preventive mechanism.
In the second aspect, the invention is intended to provide an oil-based ink composition for use in a ball-point pen having smooth feel of writing, and excellent in the improvement of the fastness, the coloring property and the dispersion stability of the pigment and having a back-flow-preventive mechanism therein, different from the conventional method, and an oil-based ball-point pen having a back-flow-preventive mechanism and using the oil-based ink composition described above.